Craigslist

Remember how cool the Recycler was for finding decent used things in your area? Now, take that, make it 1000 times easier to search, and make it nationwide. That's Craigslist. You can find nearly new items for the fraction of the cost you'd pay otherwise, plus look for services, find jobs, offer jobs and many more things. It's one of those things that reminds you why the web is cool in the first place